Many electronic devices such as computers, compact disc players, DVD players, and the like include a drive assembly or housing wherein a disk is coaxially mounted about a spindle apparatus that rotates at speeds in excess of several thousand revolutions per minute (RPM) and a head that writes and reads information to and from the rotating storage disk. The head usually is disposed at the end of an actuator arm and positioned above the storage disk. The actuator arm can move relative to the storage disk. In many instances, the drive assembly is mounted on a disk base (support plate) and sealed with a cover plate to form a housing that protects the assembly from contamination.
Serious damage including loss of valuable information, can result from migration of gaseous and particulate contaminants into the drive assembly housing. To prevent or substantially reduce introduction of these contaminants into the drive housing, a flexible sealing gasket is disposed between the mounting plate and the cover plate. Sealing gaskets typically are prepared by punching annular disks from a sheet of cured elastomer.
These sealing gaskets typically are adhered or mechanically attached, e.g., affixed with screws, to the support plate. Not only do these means of attachment present long-term problems, they present many manufacturing issues. To begin with, the pre-formed gasket must be properly seated into the assembly to ensure a proper seal. And, once seated, the mechanical fasteners must be affixed into place. Or, where an adhesive is employed, the gasket must be treated with the adhesive prior to placement in the assembly or the adhesive must be placed directly in the assembly. These manufacturing steps not only add time and cost to the manufacturing process, but they also present quality assurance issues.
An alternative solution includes the use of an adhesive material that can be directly applied to the support plate or cover plate prior to or after assembly of the housing. For example, a material can be extruded onto the cover plate prior to affixing the cover plate to the support. A first requirement of this material is that is must adhere to the cover plate. The cover plate is typically made of metal or other polar materials and therefore the number of materials that can be employed is necessarily limited. Materials such as polyamides (e.g., nylon 12) are known to adhere to polar surfaces. Unfortunately, many of these materials are thermoplastic in nature and tend to be rather hard. Therefore, their ability to act as gaskets is rather limited.
Softer compositions that include nylon are known. For example, U.S. Pat. No. 6,300,418 teaches compositions that include a styrene-based thermoplastic elastomer such as styrene-butadiene-styrene, styrene-ethylene/butylene-styrene, or styrene-isoprene-styrene and an adhesion promoter such as the reaction product between a functionalized thermoplastic rubber and a polyamide. Unfortunately, the service temperature of these blends is rather low and therefore they are inferior in many applications including their use in the formation of gaskets for electronic devices. Indeed, electronic devices can be exposed to temperatures in excess of 70° C., and even potentially 70° C., which will cause thermoplastic elastomer copolymers such as styrene-butadiene-styrene or styrene-isoprene-styrene to flow. As a result, the gaskets will deleteriously deform.